Processing X/K band radio occultation data in the presence of turbulence

Abstract

Canonical transform (CT) and full‐spectrum inversion (FSI) methods can be used in processing radio occultation data to retrieve transmission profiles, which are necessary in addition to bending angle profiles for the retrieval of atmospheric humidity independent of temperature. Low Earth orbiter–low Earth orbiter cross‐link occultations with X/K band frequencies can provide transmission data along the wing of the 22 GHz water vapor absorption line. The computation of transmission assumes spherical symmetry of the atmospheric real and imaginary refractivity. This condition is broken in the presence of turbulence, which can result in significant errors in transmission. We suggest the computation of the differential transmission from the differential CT/FSI amplitude to correct for the effect of turbulence. The efficiency of the method is tested by quasi‐realistic numerical end‐to‐end simulations. We explicitly modeled turbulence as random refractivity fluctuation field based on power form of the fluctuation spectrum. The simulations demonstrate that the error in the retrieved transmission can be significant in a single frequency channel, while the differential transmission can be retrieved with high accuracy. The new method does not impose any significant restriction on the frequency difference between the channels and provides very good differential transmission sensitivity if spacings of a few gigahertz are chosen (e.g., 10 and 17 GHz or 17 and 20 GHz).